![Page 1: Chapter 6 Factors controlling geomorphic response to large floods.adpc.net/casita/Course Modules/Flood vulnerability... · 2015-08-27 · Chapter 6 Factors controlling geomorphic](https://reader031.vdocuments.us/reader031/viewer/2022011902/5f0d6d4a7e708231d43a4cec/html5/thumbnails/1.jpg)
2/18/2003N.C.KINGMA1
Chapter 6Factors controlling geomorphic
response to large floods.Drs. Nanette C. Kingma
![Page 2: Chapter 6 Factors controlling geomorphic response to large floods.adpc.net/casita/Course Modules/Flood vulnerability... · 2015-08-27 · Chapter 6 Factors controlling geomorphic](https://reader031.vdocuments.us/reader031/viewer/2022011902/5f0d6d4a7e708231d43a4cec/html5/thumbnails/2.jpg)
2/18/2003N.C.KINGMA2
Factors controlling geomorphic response to large floods.
Large floods; T≥ 50 yr;The reponse is controlled by:
Drainage basin factors (I)River channel factors (II)
(or called Network, Basin and Channel factors).
![Page 3: Chapter 6 Factors controlling geomorphic response to large floods.adpc.net/casita/Course Modules/Flood vulnerability... · 2015-08-27 · Chapter 6 Factors controlling geomorphic](https://reader031.vdocuments.us/reader031/viewer/2022011902/5f0d6d4a7e708231d43a4cec/html5/thumbnails/3.jpg)
2/18/2003N.C.KINGMA3
I. Drainage basin factors.
Controls on the river that are external to the channel and floodplain ; including;
climatological factors (mainly rainfall regime);hydrology (mainly peak discharge, contributing area, and hydrograph reponse)basin morphometry;sediment load;vegetation;soils;bedrock.
![Page 4: Chapter 6 Factors controlling geomorphic response to large floods.adpc.net/casita/Course Modules/Flood vulnerability... · 2015-08-27 · Chapter 6 Factors controlling geomorphic](https://reader031.vdocuments.us/reader031/viewer/2022011902/5f0d6d4a7e708231d43a4cec/html5/thumbnails/4.jpg)
2/18/2003N.C.KINGMA4
II. River channel factors.
Internal controls on the river resulting from physical characteristics of the channel and flow, including:
channel gradient;channel and floodplain geometry;channel morphology;bank cohesion.
![Page 5: Chapter 6 Factors controlling geomorphic response to large floods.adpc.net/casita/Course Modules/Flood vulnerability... · 2015-08-27 · Chapter 6 Factors controlling geomorphic](https://reader031.vdocuments.us/reader031/viewer/2022011902/5f0d6d4a7e708231d43a4cec/html5/thumbnails/5.jpg)
2/18/2003N.C.KINGMA5
Ad 1.2. Hydrologic factors:
Contributing Drainage Area:extremely variable:arid/semi-arid often CDA minor portion of drainage basin; If small contributing area producing large flood
large amount of rainfall; high intensity; short duration flash flood.humid regions: widespread rainfall over entire drainage basin.
![Page 6: Chapter 6 Factors controlling geomorphic response to large floods.adpc.net/casita/Course Modules/Flood vulnerability... · 2015-08-27 · Chapter 6 Factors controlling geomorphic](https://reader031.vdocuments.us/reader031/viewer/2022011902/5f0d6d4a7e708231d43a4cec/html5/thumbnails/6.jpg)
2/18/2003N.C.KINGMA6
Ad 1.2. Hydrologic factors:
Peak Discharge & Flash Flood Magnitude Index:
Q peak absolute not so important; more important ratio Q max peak / Q mean annual discharge the morphology of many rivers is adjusted to most commonly experienced flow (bankfull) for humid regions; in contrast with semi-arid regions adjustment often to the less frequent large floods;
Flash flood indexFlash flood index developed in the US.
![Page 7: Chapter 6 Factors controlling geomorphic response to large floods.adpc.net/casita/Course Modules/Flood vulnerability... · 2015-08-27 · Chapter 6 Factors controlling geomorphic](https://reader031.vdocuments.us/reader031/viewer/2022011902/5f0d6d4a7e708231d43a4cec/html5/thumbnails/7.jpg)
2/18/2003N.C.KINGMA7
AD.I.2 Hydrologic factors:FFMI
High Flash Flood Magnitude Index (FFMI)indicates the likelihood of streams experiencing major geomorphic changes in large floods.
![Page 8: Chapter 6 Factors controlling geomorphic response to large floods.adpc.net/casita/Course Modules/Flood vulnerability... · 2015-08-27 · Chapter 6 Factors controlling geomorphic](https://reader031.vdocuments.us/reader031/viewer/2022011902/5f0d6d4a7e708231d43a4cec/html5/thumbnails/8.jpg)
2/18/2003N.C.KINGMA8
Ad I.2 : Hydrologic factors:FFMI
Results of index “checked” with observations of large floods whether or not major geomorphic changes occurred.
Result: also other factors play a role: topography, vegetation / lithology / basin morphometry !!
![Page 9: Chapter 6 Factors controlling geomorphic response to large floods.adpc.net/casita/Course Modules/Flood vulnerability... · 2015-08-27 · Chapter 6 Factors controlling geomorphic](https://reader031.vdocuments.us/reader031/viewer/2022011902/5f0d6d4a7e708231d43a4cec/html5/thumbnails/9.jpg)
2/18/2003N.C.KINGMA9
Example; basin study after hurricane Camille.
Downstream valley widening related to upstream debris avalanches;
high supply of coarse bed load (1)steep gradients (2)basin shape(3)
![Page 10: Chapter 6 Factors controlling geomorphic response to large floods.adpc.net/casita/Course Modules/Flood vulnerability... · 2015-08-27 · Chapter 6 Factors controlling geomorphic](https://reader031.vdocuments.us/reader031/viewer/2022011902/5f0d6d4a7e708231d43a4cec/html5/thumbnails/10.jpg)
2/18/2003N.C.KINGMA10
Upstream - down stream effects.
![Page 11: Chapter 6 Factors controlling geomorphic response to large floods.adpc.net/casita/Course Modules/Flood vulnerability... · 2015-08-27 · Chapter 6 Factors controlling geomorphic](https://reader031.vdocuments.us/reader031/viewer/2022011902/5f0d6d4a7e708231d43a4cec/html5/thumbnails/11.jpg)
2/18/2003N.C.KINGMA11
Ad I.3 Basin morphometry.
Basin shape influences hydrograph.(see chapter 2; equidimensional versus elongated
Ruggedness number: drainage density * relief;
Basin magnitude;high first order stream frequency;sparse vegetation ; thin soilsMost important factors in explaining variation in peak discharges; when similar climatic regions concerned.
![Page 12: Chapter 6 Factors controlling geomorphic response to large floods.adpc.net/casita/Course Modules/Flood vulnerability... · 2015-08-27 · Chapter 6 Factors controlling geomorphic](https://reader031.vdocuments.us/reader031/viewer/2022011902/5f0d6d4a7e708231d43a4cec/html5/thumbnails/12.jpg)
2/18/2003N.C.KINGMA12
Drainage basin morphometry
![Page 13: Chapter 6 Factors controlling geomorphic response to large floods.adpc.net/casita/Course Modules/Flood vulnerability... · 2015-08-27 · Chapter 6 Factors controlling geomorphic](https://reader031.vdocuments.us/reader031/viewer/2022011902/5f0d6d4a7e708231d43a4cec/html5/thumbnails/13.jpg)
2/18/2003N.C.KINGMA13
II. River channel factors
1.1 Channel gradient & bedload:channel bank and floodplain erosion is facilitated by high velocity flows carrying coarse bedload materials that can be used as abbrasive tools)
Lithology + Climate⇒control on sediment sizeLithology ⇒control on channel gradient; resistant rock often steeper gradients.
![Page 14: Chapter 6 Factors controlling geomorphic response to large floods.adpc.net/casita/Course Modules/Flood vulnerability... · 2015-08-27 · Chapter 6 Factors controlling geomorphic](https://reader031.vdocuments.us/reader031/viewer/2022011902/5f0d6d4a7e708231d43a4cec/html5/thumbnails/14.jpg)
2/18/2003N.C.KINGMA14
Channel geometry
Plays important role in determining geomorphic effect of large floods.
Increased flood discharges in bedrock channel accomodated by dramatic depth increasse +veloclity increase ⇒ results in macro turbulent flow phenomena.Enormous capacity to transport large sediment amounts; e.g. large bouldersresults finally in significant erosion of channel wall & floor by macro turbulent flow!!
![Page 15: Chapter 6 Factors controlling geomorphic response to large floods.adpc.net/casita/Course Modules/Flood vulnerability... · 2015-08-27 · Chapter 6 Factors controlling geomorphic](https://reader031.vdocuments.us/reader031/viewer/2022011902/5f0d6d4a7e708231d43a4cec/html5/thumbnails/15.jpg)
2/18/2003N.C.KINGMA15
Channel geometry
Often no effect due to high boundary resistance of bedrock channel walls.
![Page 16: Chapter 6 Factors controlling geomorphic response to large floods.adpc.net/casita/Course Modules/Flood vulnerability... · 2015-08-27 · Chapter 6 Factors controlling geomorphic](https://reader031.vdocuments.us/reader031/viewer/2022011902/5f0d6d4a7e708231d43a4cec/html5/thumbnails/16.jpg)
2/18/2003N.C.KINGMA16
Check list
![Page 17: Chapter 6 Factors controlling geomorphic response to large floods.adpc.net/casita/Course Modules/Flood vulnerability... · 2015-08-27 · Chapter 6 Factors controlling geomorphic](https://reader031.vdocuments.us/reader031/viewer/2022011902/5f0d6d4a7e708231d43a4cec/html5/thumbnails/17.jpg)
2/18/2003N.C.KINGMA17
Temporal ordering of geomorphic effects.
Responses to floods of equal magnitudeand frequency vary greatly depending on temporal ordering of events !!
1954 flood dramatic redistribution of channel gravel and erosion of fine grained terraces;
1974 flood only minor redistribution of fluvial sediments.
From: Flood Geomorphology
![Page 18: Chapter 6 Factors controlling geomorphic response to large floods.adpc.net/casita/Course Modules/Flood vulnerability... · 2015-08-27 · Chapter 6 Factors controlling geomorphic](https://reader031.vdocuments.us/reader031/viewer/2022011902/5f0d6d4a7e708231d43a4cec/html5/thumbnails/18.jpg)
2/18/2003N.C.KINGMA18
Conclusions.
It’s difficlult to make prediction of expected channel response.
Basin-, network and Channel factors interact.Man’s influence excluded (influence on sediment load, discharge, channel gradient, channel geometry etc.)
![Page 19: Chapter 6 Factors controlling geomorphic response to large floods.adpc.net/casita/Course Modules/Flood vulnerability... · 2015-08-27 · Chapter 6 Factors controlling geomorphic](https://reader031.vdocuments.us/reader031/viewer/2022011902/5f0d6d4a7e708231d43a4cec/html5/thumbnails/19.jpg)
2/18/2003N.C.KINGMA19
Major trends.
Major trend:i.e. important variables:
1. Climate: intensity - duration frequency intensity rainfall;
2. River hydrology: factors relating to flashiness of hydrograph;
3. Basin morphometry: Factors having an effect on the flashiness of hydrograph.
![Page 20: Chapter 6 Factors controlling geomorphic response to large floods.adpc.net/casita/Course Modules/Flood vulnerability... · 2015-08-27 · Chapter 6 Factors controlling geomorphic](https://reader031.vdocuments.us/reader031/viewer/2022011902/5f0d6d4a7e708231d43a4cec/html5/thumbnails/20.jpg)
2/18/2003N.C.KINGMA20
Streams experiencing major geomorphic change.
Streams experiencing major geomorphic change ( and less dependent on climate) are characterised by:1. Flashy hydrograph; 2. High channel gradient;(relation to lithology ;
tectonics)3. Abundant coarse load;4. Relatively low bank cohesion5. Channel cross sections enabling deep, high
velocity flows where macro turbulence can be initiated and maintained.
![Page 21: Chapter 6 Factors controlling geomorphic response to large floods.adpc.net/casita/Course Modules/Flood vulnerability... · 2015-08-27 · Chapter 6 Factors controlling geomorphic](https://reader031.vdocuments.us/reader031/viewer/2022011902/5f0d6d4a7e708231d43a4cec/html5/thumbnails/21.jpg)
2/18/2003N.C.KINGMA21
Important factors controlling channel and floodplain response to large magnitude floods.
![Page 22: Chapter 6 Factors controlling geomorphic response to large floods.adpc.net/casita/Course Modules/Flood vulnerability... · 2015-08-27 · Chapter 6 Factors controlling geomorphic](https://reader031.vdocuments.us/reader031/viewer/2022011902/5f0d6d4a7e708231d43a4cec/html5/thumbnails/22.jpg)
2/18/2003N.C.KINGMA22
Geomorphic work.
Two different perceptions exist;1. Measured as the amount of transported
load;2. Modification of landforms also called
geomorphic effectiveness.
![Page 23: Chapter 6 Factors controlling geomorphic response to large floods.adpc.net/casita/Course Modules/Flood vulnerability... · 2015-08-27 · Chapter 6 Factors controlling geomorphic](https://reader031.vdocuments.us/reader031/viewer/2022011902/5f0d6d4a7e708231d43a4cec/html5/thumbnails/23.jpg)
2/18/2003N.C.KINGMA23
Future studies.
Increased effort is needed to determine the true recurrence interval of large floods.Multivariate statistical techniques may be necessarry to understand the complex interactions of channel response to large floods.